VARIATION 433 



unified individualities, experiment internally, not fortui- 

 tously but artistically, not at random nor yet inexorably, 

 not purposefully but perhaps purposively, and that they are 

 body-minds or mind-bodies telescoped down? 



In certain moods one feels inclined to agree with those 

 who say to-day what Darwin said more than fifty years 

 ago that our ignorance of variation is profound, and who 

 urge the appropriateness of silence. Yet perhaps it is more 

 wholesome for thinkers to have an exposure of the vast un- 

 certainty that surrounds this central problem of biology than 

 to be led astray by those who confidently declare that organic 

 evolution can be mechanically re-described. If the re-descrip- 

 tion is difficult and still impossible when we use full-blooded 

 biological categories, how must it be if matter-and-motion 

 categories are supposed to be the only legitimate ones ? 



SUMMARY. 



The central and most difficult problem of aetiology concerns the 

 origin of the new, that is, of those variations or mutations that form 

 the raw materials of progress or the reverse. 



From an unbiassed registration of all observed differences between 

 the members of the same species there have to be subtracted all the 

 peculiarities that can be reasonably interpreted as associated with 

 age and sex, or as individually-acquired somatic modifications di- 

 rectly due to peculiarities of nurture, whether environmental, nutri- 

 tional, or functional. As there is no convincing evidence at present 

 that these extrinsic somatic modifications can be transmitted as such, 

 or in any representative degree, they cannot be included, in the 

 first instance at least, among the raw materials of racial evolution. 

 These are discerned when the modifications in question and the 

 peculiarities associated with age and sex are subtracted from the 

 total of observed differences. For this subtraction brings into view 

 the true variations or mutations inborn not acquired, blastogenic 

 not somatogenic, endogenous not exogenous, expressions or outcomes 

 not indents or imprints. Some at least are very transmissible, and 

 these furnish the raw materials of evolution. 



